The present invention relates to very low cost portable compact scanners and printers. More particularly it is directed to a removable ribbon cassette and drive system accessary and method for use with a portable compact scanner copier/printer which facilitates simple ribbon replacement by consumers. In addition, the present invention relates to an improved thermal transfer printing process wherein the separating of the spent thermal transfer ribbon from the receiver sheet is enhanced by an "L" shaped mechanical member pivotally connected to a translatable thermal print head. Yet still, the present invention relates to methods of ribbon conservation.
Historically, copies of original documents have been produced by a xerographic process wherein the original document to be copied is placed on a transparent platen, either by hand or automatically through the use of a document handler, and the original document illuminated by a relatively high intensity light. Image rays reflected from the illuminated document are focused by a suitable optical system onto a previously charged photoconductor, the image light rays functioning to discharge the photoconductor in accordance with the image content of the original to produce an electrostatic latent image of the original on the photoconductor. The electrostatic latent image so produced is thereafter developed by a suitable developer material commonly referred to as toner, and the developed image transferred to a sheet of copy paper brought forward by a suitable feeder. The transferred image is thereafter fixed to the copy paper by fusing to provide a permanent copy while the photoconductor is cleaned of residual developer preparatory to recharging.
More recently, interest has arisen in electronic imaging where, in contrast to the aforedescribed xerographic system, the image of the document original is converted to electrical signals which may be processed, transmitted over long distances, and/or stored, are used to produce one or more copies. In such an electronic imaging system, rather than focusing the light image onto a photoreceptor for purposes of discharging a charged surface prior to xerographic development, the optical system focuses the image rays reflected from the document original onto an image reading array which serves to convert the image rays reflected to electrical signals. These signals are used to create an image by some means such as operating a laser beam to discharge a xerographic photoreceptor, or by operating some direct marking system such as an ink jet or thermal transfer printing system.
It is generally advantageous if the normally separate document reading and copy printing operations could be combined. If some of these reading/writing functions could be combined, system operation and synchronization could be simplified and system cost reduced through the use of fewer parts.
There are systems in the prior art that address the above identified concerns. For example, U.S. Pat. Nos. 4,496,984 and 4,583,126 to Stoffel, disclose an input/output scanner for simultaneously reading a document and writing a copy thereof. The document and copy sheet are fed in back to back relation with respect to a read/write station. A monolithic full width reading array scans each line in two steps, to improve resolution. The writing array of the read/write station consists of rows of ink jet nozzles, of which the number and disposition is in direct correspondence to the sensors of the read bar/array.
U.S. Pat. No. 4,424,524 to Danisle discloses a full width read/write LED array for scanning a document in the read mode or exposing the photoreceptor in the write mode. A Selfoc optical fiber lens array is used for focusing the full width LED array on the document or photoreceptor.
U.S. Pat. No. 4,724,490 to Tanioka teaches an image input device having an original exposing portion, an image sensor portion, and a thermal print head portion formed by heat generating members. The heat generating members are driven by a signal originating in the image sensor portion and are used to effect printing using a thermosensitive copy medium.
A difficulty with these prior art systems combining imaging and printing is the complexity and cost of separate components such as the complex optics, photoreceptor and developer such as in the Daniele system. In others such as the Stoffel system, it is necessary for an operator to manually combine a document and copy sheet into a single unit for manual insertion to machine feed rolls. Such a system also has a significant cost penalty associated with components such as the monolithic full width reading array.
Several patents assigned to the assignee of the instant application suggest a unique compact alternative to the above-described systems. These include U.S. Pat. Nos. 4,920,421, 5,040,074, 5,032,922, 5,153,736, 5,153,738, 5,162,918 and 5,187,588, all of which teachings are incorporated herein by reference.
The copier concepts described immediately above are attempts to reduce cost and complexity of such a copier while at the same time maximizing compactness and portability. Accordingly, all of the systems described therein rely on ink jet or thermal transfer print technology rather than the more bulky impact type printing apparatus.
Printing with ink jets requires specialized nozzles no which ink is supplied under pressure by a pump from a suitable manifold or other type of reservoir. Generally, the print heads of these systems are connected to a flexible umbilical ink supply tube. Of course, this extra hardware adds to the overall cost of the copier and unnecessarily complicates the print mechanism.
Thermal printing, on the other hand, is a non-impact printing process that enables formation of high resolution images. These printing processes are simple, offer low noise levels, and are very reliable over extended usages. Thermal printing processes may be classified into three categories. Direct thermal printing entails the imagewise heating of special papers coated with heat sensitive dyes, such that an image forms in the heated areas. Another method of thermal printing is known as the dye transfer or dye sublimation technique, and operates by heating a transfer element coated with a sublimable dye, which transfer element is not in contact with the receiving sheet. When the transfer element is imagewise heated, the dye sublimates and migrates to the receiver sheet, which possesses a polymeric coating into which the dye diffuses, forming the image. A third method of thermal printing is known as thermal transfer printing. The thermal transfer printing process entails imagewise heating of a transfer element containing ink. The transfer element is in intimate contact with a heater or heating element on one surface and a blank receiving sheen on the other surface. Imagewise heating of the transfer element affects the ink in such a way as to cause it to transfer from the transfer element to the receiving sheet, thereby resulting in image formation. Thermal transfer printing methods generally employ uncoated plain papers, which enables prints with acceptable appearance and excellent archival properties. In addition, the thermal transfer printing method can be employed for color printing applications by using transfer elements of the desired color or color combinations.
Thermal transfer printing processes generally employ a thermal printhead, a transfer element, and a receiver sheet. The side of the transfer element containing the ink is placed in contact with the receiver sheet, and heat originating from the printhead is then applied to the transfer element. Heat conducted through the element increases the temperature of the ink, which can cause it to melt, soften, decrease in viscosity, or otherwise undergo a transition that enables the ink to transfer to the receiver sheet. After the receiver sheet and transfer element are separated, an image remains on the receiver sheet. The operation of separating the transfer element from the receiver sheet, however, is critical in obtaining a crisp and smudge free copy product.
An alternative method of heating the transfer element, known as resistive heating, employs an array of electrodes instead of a thermal printhead to generate a current between the electrodes and a grounded conductive layer in the transfer element. This method is described in the IBM Journal of Research & Development, Vo. 29, No. 5, 1985, the disclosure of which is incorporated herein by reference. Additional information concerning thermal transfer printing processes is disclosed in Thermal Transfer Printing: Technology, Products, Prospects, published by Datek Information Services, P.O. Box 68, Newtonville, Mass., the disclosure of which is also incorporated herein by reference. Resistive heating methods also critically depends on a definite separating of the transfer element from the receiver sheet for obtaining a crisp final copy product.
As pointed out above, the process of stripping the transfer element from receiver sheet is an important consideration in portable thermal printers. However, perhaps equally significant is the tradeoff between i) the number of pages which can be printed before it becomes necessary to replace the thermal transfer element and ii) the bulk or overall physical size of the cassette structure carrying the transfer element on spools therein. This tradeoff is common to both portable thermal printers and copiers of the type described above.
One obvious method of increasing the number of successive documents created is to silly enlarge the thermal transfer element spool capacity within the cassette structure. However, generally, the length of the transfer element ribbon is proportional to the square of its spool diameter. For prior art systems using ribbon cassettes which move with the print head as illustrated in FIG. 1A to quadruple the ribbon capacity requires adding as much as one inch (1") to the ribbon cassette footprint height and one half inch (0.5") to the footprint width such as demonstrated in FIG. 1A. This results in an increase in volume of forty-two percent (42%) in the resultant size target copier/printer apparatus as best shown in FIG. 2B. The cassette according to the present invention allows for growth without impact on the overall size of the target printer/copier apparatus (FIG. 1C).